Various impact attenuation devices and energy absorbing systems have been used to prevent or reduce damage resulting from a collision between a moving motor vehicle and a fixed roadside hazard or obstacle. Examples of prior impact attenuation devices and energy absorbing systems include crash cushions or crash barriers with various structures and containers having crushable elements. Other crash barriers rely on inertia forces generated when material such as sand is accelerated during an impact to absorb energy.
Some of these devices and systems have been developed for use at narrow roadside hazards or obstacles such as at the end of a median barrier, end of a barrier extending along the edge of a roadway, large sign posts adjacent to a roadway, and bridge pillars or center piers. Such impact attenuation devices and energy absorbing systems are installed in an effort to minimize the extent of personal injury as well as damage to an impacting vehicle and any structure or equipment associated with the roadside hazard.
Examples of general purpose impact attenuation devices are shown in U.S. Pat. No. 5,011,326 entitled Narrow Stationary Impact Attenuation System; U.S. Pat. No. 4,352,484 entitled Shear Action and Compression Energy Absorber; U.S. Pat. No. 4,645,375 entitled Stationary Impact Attenuation System; and U.S. Pat. No. 3,944,187 entitled Roadway Impact Attenuator. Examples of specialized stationary energy absorbing systems are shown in U.S. Pat. No. 4,928,928 entitled Guardrail Extruder Terminal and U.S. Pat. No. 5,078,366 entitled Guardrail Extruder Terminal. Each of the preceding patents is incorporated by reference for all purposes in the present application.
Examples of impact attenuation devices and energy absorbing systems appropriate for use on a slow moving or stopped highway service vehicle are shown in U.S. Pat. No. 5,248,129 entitled Energy Absorbing Roadside Crash Barrier; U.S. Pat. No. 5,199,755 entitled Vehicle Impact Attenuating Device; U.S. Pat. No. 4,711,481 entitled Vehicle Impact Attenuating Device; U.S. Pat. No. 4,008,915 entitled Impact Barrier for Vehicles.
Recommended procedures for evaluating performance of various types of highway safety devices including crash cushions is presented in National Cooperative Highway Research Program (NCHRP) Report 350. A crash cushion is generally defined as a device designed to safely stop an impacting vehicle within a relatively short distance. NCHRP Report 350 further classifies crash cushions as either "redirective" or "nonredirective". A redirective crash cushion is designed to contain and redirect a vehicle impacting downstream from a nose or end of the crash cushion facing oncoming traffic extending from a roadside hazard. Nonredirective crash cushions are designed to contain and capture a vehicle impacting downstream from the nose of the crash cushion. Redirective crash cushions are further classified as either "gating" or "nongating" devices. A gating crash cushion is one designed to allow controlled penetration of a vehicle during impact between the nose of the crash cushion and the beginning of length of need (LON) of the crash cushion. A nongating crash cushion is designed to have redirection capabilities along its entire length.